Process for the preparation of electrophotographic reversed images



United States Patent lice sequently, the material is exposed to light under a master,

or by episcopic means, whereby the charge leaks away in the parts struck by light, and an invisible electrostatic image corresponding to the master is formed. This is made visible by contacting it with a resin powder which can be suspended in a solvent and which has an electric charge opposite to that of the electrostatic image, and then fixed directly or after transferring to a transfer sheet by the action of heat or by another method known per se.- It has already been attempted to produce reversed images by the application of developers which contain a resin powder having the same charge as the electrostatic image on the electrophotographic reproduction material. This method does not lead to satisfactory results, because marginal eifects appear, i.e. the outlines of the charged areas of the electrophotographic reproduction material show sharp and strong contours, which diminish towards the uncharged parts. Larger black areas with good coverage are difiicultly obtained.

No satisfactory improvement in the coverage of black surfaces is obtained by applying electric fields to this reversal process.

Now a method has been found for the preparation of electrophotographic reversed images which comprises electrostatically charging, in the absence of flight, the photoconductive layers of electrocopying material, exposing to a light-image and developing the light-struck areas of the photoconductive layer by a brief contact with a finely divided resin having the same electric charge as the areas of the photoconductive layers which were not struck by light, and finally fixing the developed image, the process being characterized in that the photoconductive layer contains at least one wax. Suitable waxes to be added to the photoconductive layers, according to the invention, are natural or synthetic waxes, such as montan wax, sperm wax, wool wax, beeswax, gheddie wax, Japan wax, China wax, shellac wax, carnauba wax, candelilla wax, so-called A-wax, QP-wax, SPO-wax, V-wax, and the products commercially available as Gersthofener Wachse and marked as O, KP, S and L waxes. Preferably, solid natural waxes, such as rnontan wax, beeswax, carnauba wax and the above listed solid synthetic Gersthofener Wachse are used. According to the invention, the waxes are added in quantities of about 3 percent to about 20 percent, preferably of about 7 percent to about 10 percent calculated on the weight of the photoconductive substances. According to the statements made by Ullmann in Enzyklopaedie der T echnischen Chemie, 2nd edition, 1932, vol. 10, page 293, the waxes may contain small amounts of free fatty acids or free alcohols, respectively. Accordingly, synthetic waxes which contain such products, or to which such products have been added, are also within the scope of the present invention.

As photoconductors, substances are used which are usually applied in the photoelectric process, especially organic photoconductors, such as oxadiazoles, e.g. 2,5-bis- (p-dialkyl-amino-phenyl)-1,3,4-oxadiazole; triazoles, e.g. 2,5 bis-(p-dialkylamino-phenyl)-l,3,4-triazole; azometh ines, e.g. the products obtained from p-phenylenediamine 3,159,483 7 Patented Dec. 1, 1964 .and p-dialkyl-aminobenzaldehyde; aromatic hydrocarlbons containing at least four benzene nuclei, e.g. benzanthrene, or chrysene; imidazolones, e.g. l,3,4,5-tetraphenylimidazolone; pyrazolones, e.g. 1,3,5-triphenylpyrazolone; tetrahydroimidazole; oxazoles, e.g. 2,5-diphenyloxazole or Z-(p-dialkylamino-phenyl)-4,5-diphenyloxazole; cyclo-azaoctatetraene-derivatives, e.g. 1,2,5,6-tetraazacyclooctatetraene-2,4,6,8; stilbene derivatives, e.g. 4- dialkyl-amino-4'-nitrilostilbene; fluorene derivatives, e.g. 2,3,5-triphenyl-fluorene; thiophene derivatives, e.g. 2,3,5- triphenylthiophene; pyrrole derivatives, e.g. 2,3,5-triphenylpyrrole; triphenylamine derivatives, e.g. triphenylamine and its alkyl derivatives; moreover, highly polymeric substances, such as polymeric vinyl carbazole, polyindene, polyacenaphthene, polyvinylnaphthalene, and polyvinylquinoline. Mixtures of photoconductors can also be used. 7

Furthermore, it may be advantageous in the preparation of the photoconductive layer to use the photoconductors and the Waxes in admixture with natural and/or synthetic resins. Suitable resins are, for instance: balsam resins, colophony, shellac, colophony-modified phenol resins, and other resins of which colophony constitutes the major part, further, coumarone resins, indene resins and the materials covered by the collective term synthetic lacquer resins which include processed natural substances, such as cellulose ether, polymers, such as vinylpolymers, e.g. polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl acetals, polyvinyl ethers, polyacrylic and polymethacrylic acid esters, also polystyrene and polyisobutylene, chlorinated caoutchouc, polycondensates, e.g. polyesters such as phthalate resin,

' alkyd resin, maleic acid resin, maleic acid/colophony mixed esters of higher alcohols, phenolformaldehyde resin, particularly colophony-modified phenol-formaldehyde condensates, urea-formaldehyde condensates, malamineformaldehyde resins, aldehyde resins, ketone resins, especially the so-called AW 2-resins, xylene-formaldehyde resins, polyamides, and polyadducts, such as polyurethanes. Further, there are used polyolefins, such as polyethylenes, polypropylene and phthalic acid polyesters, e.g. terephthalic acid/isophthalic acid/ethyleneglycol polyesters.

When using the photooonductive compounds in admixture with the above described resins, the proportions of resin and photoconductive substance can vary widely, but the content of photoconductive substance should be at least 20%. Preferably, mixtures are used which contain from 2 parts by weight of resin and 1 part by Weight of pho toconductive substance to 2 parts by weight of photoconductive substance and 1 part by weight of resin. The use of mixtures containing about equal parts of the two components has been found to be advantageous.

The electrophotographic reproduction material used in the present procedure is prepared by coating a support with the above described photoconductors in admixture with the waxes and eventually with the resins, preferably dissolved in an organic solvent; the solution is e.g. cast, coated or sprayed onto the support and then the solvent is evaporated.

The products can also be applied in the form of aqueous or non-aqueous dispersions. Furthermore, it is possible ,to first apply the photoconductive layerfor example together with resinsto the support, and then to cover the photoconductor with a thin wax layer. This may be performed by a simple rubbing in, for example by means of a cloth or a roller. The Wax can also be applied when dissolved in a solvent.

The base materials used as supports may be any that satisfy the requirements of eleotrophotography, e.g. metal or glass plates, paper or plates or foils made of electroconductive resins or plastics, such as polyvinyl alcohol,

polyarnides, and polyurethanes. Other plastics which have the required electroconductivity, such as cellulose acetate and cellulose, butyrate, especially in a partially saponified form, polyesters, polycarbonates, and polyolefines, if they are covered with an electroconductive layer or if they are converted into electroconductive materials, e.g. by chemical treatment or by introduction of materials which render them electrically conductive, may also be used. Generally speaking, electroconductive supports are suitable for the purposes of the present invention. In the sense of the present invention, the term electroconductive support comprises materials having a specific conductivity higher than 10- ohm* .cm.- preferably higher than lO ohm hcmf' The base material described above, provided with a thin coherent layer of uniform thickness of the photoconduotive layer according to the present invention, is used for electrophotographically producing reversed images by applying to the photoconductive layer, in the absence of light, an overall positive or negative charge, for example by means of a corona discharge taken from a charging device maintained at about 6000 to 7000 volts. Subsequently, the electrophotographic material is exposed to light, either in contact with a master or by episcopic or diascopic projection of a master. An electrostatic image corresponding to the master is thus obtained. This invisible image is developed to a visible reversed image by contacting it,.with a developer, e.g. consisting of a carrier and a toner, the charge of the toner having the same polarity as the electrostatic image to be developed. Suitable carriers are tiny glass balls, iron powder, inorganic crystals, such as sodium chloride, potassium chloride, or sodium sulfate, crystals of organic substances, such as anthracene, fiuorene, indene, starch in the shape of balls, or glass balls coated with a resin, or tiny balls of plastic material. The toner consists of a resin-carbon black mixture, or of a colored resin. The toner is usually applied in a grain size of about 1100,u, preferably of about -30 In any case, a developer is used in which the charge of the toner has the same polarity as that originally given to the photoconductive layer by means of the corona discharge.

The reversed image which has been made visible by development is fixed, e.g. by heating it with an infrared radiator, to a temperature of 100170 C., preferably 120-150" C., or by treatment with solvents, such as trichloroe thylcne, carbon tetrachloride, ethyl alcohol or steam. Images are thus obtained which are negatives of the master, the dark portions being uniformly colored.

These electrophotographic images may also be transformed into printing plates. For this purpose, they are wiped over with a suitable solvent or with a developer liquid, preferably an alkaline aqueous developer, rinsed with Water and inked with greasy ink. Printing plates are thus obtained which may be clamped to an offset printing machine and used for printing.

If transparent supports are used, the electrophotographic images can also be used as masters for the pro duction of additional copies on any type of layers. Likewise, when using translucent supports for the photoconductive layers provided by the present invention, images may also be produced by a reflex process.

The photoconductive layers of the present invention absorb light primarily within the ultraviolet range of the spectrum. The sensitivity of the photoconductive layers can be improved by the addition of activating substances. Such activators are organic substances which in molecular complexes of the donor-acceptor type (Tr-complexes, charge transfer complexes) can serve as electron-acceptors. They are compounds of a high electron affinity and are acids, according to the definition of Lewis. Substances of such nature are those containing strongly polarizing residues or groups, such as the cyano group or nitro group; halides, such as fluorine, chlorine, bromine, and iodine, the ketone group, the ester group, an acid anhydride group or acid groups such as carboxylic groups or the quinone configuration. Such polarizing electronattracting groups are described by L. F. and M. Ficser in Organic Chemistry, 2nd edition, 1950, page 604, Table I. Due to their low vapor pressure, those substances are preferred, the melting point of which is above room temperature, viz. difiicultly volatile, solid substances.

Moderately colored substances, such as quinone can be used, however, it is preferred to use colorless or only weakly colored substances. The preferred maximum of absorption of the substances is within the ultraviolet range of the spectrum, i.e. below 4,500 A. Moreover, the activator substances to be used according to the present invention should be of low molecular weight, i.e. the molecular Weight thereof should range between 50 and about 5060, preferably between about and about 1000, since with the low molecular weight activators reproducible results, with respect to sensitivity, can be obtained. Moreover, the sensitivity is maintained constant over a long time, as, contrary to the high molecular weight substances, the low molecular Weight substances do not change substantially when stored.

Such compounds are e.g.:

act 4-cliloIro-3-nitro bcnzcnc-ph0sphonic acit Dibromosuccinie acid 2,4-dichlorobcnzoic acid Dibromo-malcic acid anhydride... 9,10-dibromo anthraccnc l,5-(1ichloro-naphthalenc 1,8-dichl0ro-11aphthalcnc ZA-dinitro-Lchloro naphthalene.

3,4-dichloro-nitrobcnzcne 2,-i-dichloro-bcnzisatin 2,6-diehloro-bcnzaldchyde lTciiebromo-naphthalie acid anhybz-l-cyano-bcnzanthronc Cyanoacctic acid Z-cyano-cinnamic acid 1,5-dieyan0-naphthalcnc 3,5-dinitro-bcnzoic acid. 3,5-dinitrosalicylic acid. 2,4-dinitro-l-benzoic acid- 2,4-dinitro-l-t0luene-G-sulfonic acid. 2,6-dinitro-1-phenoli-sulfonie acid. 1,3-di1iitro-bcnzene 4,4-dinitro-diphenyl. 3-nitro-4 rnethoxy-bcnzcic acid. 4-nitro-1mcthyl-benzoic acid. 6-11itro-4-rncthyl-l-phenol-Z-sul acid. 3-nitro-2-hydroxy-l-bcnzoic acid. 2-nit o lphonol-4sulionic acid. 4-n l-phcnol-2-sulfonic acid. 3-111 io-N-butyl-carbazolc i-nitro-aiphcnyl Totranitro-fluorononc. 2,4,6-trinitro anisol anthraqumone. Anthraquinonc-2-carboxyllc acid-.. Anthraquinonc-Z-aldchyde nil tdhraquinonc-zsulfonic acid ani- 1 c. Anthraquinone-2,7-disulfonic acid. Anthraquinone-2,7-disulfonic acidbis-anilidc. Anthrnquinone-iZ-sulfonic acid dirnethylam' e. Accnaphthcnc-quinono Anthraquinonc 2 sultonic acid mcthylamidc. Aecnnphthcne-quinono-dichl0ridc. BenzoquinonclA 1,2-bcnzanthraquinonc" Bromanil 2-nitro-bcnzcnc-sulphin c ac l-chloro-4-nitronnthraquinonc. Ohloranil l-chlorcanthruquinone Cliryscnc-quinonc Thymo-quinonc o-Chloronitro-bcnzcnc. Ghloro-acctophcnonc. 2-chloro-cinna1nie acid. 2chloro-4-nitro-l-benzoic acid. 2-chloro-5- o-l-bcnzoic acid. 3-ehloro-6-nitro-l-bcnznic acid. Phthalie acid anhydridc.

Ghloro-mucoic acid. Bromo-mucoic acid. Styrcnc-dibrornide. Xylene tetra-bromide.

Triphcnyl-chloro-methane. Tctrachioro-phtlialic acid. Tctrabroniomlithalic acid. 'letraiodophthalic acid. Tctrachloro-phthalic acid anhydride.

Tctrabromo-phthalic acid anhydride.

Tctraiodo-phthalic acid anhydrid e. Tetrachlorophihalic acid monoyl-cstcr. Tctrabromo-phthalie acid monoethylestcr. Tetraiodo-phthalic acid monocthylcstcr. Iodoiorm.

Fumaric acid dinitrilc. Tctracyanoethylcnc. 1,3,5-tricyanobcnzcne.

2,4-(31 31iiiIOd-ClllOIO-IlZiDhthfllBllC. 1,4-dinitro-naphthalcnc. l,5-di.nitronaphthalcnc. 1,S-dinitro-naphthalcnc. 2-nitrobenzoic acid. 3-nitro-bcnzoic acid. 4-nitro-bcnzoic acid. 3-nitro-4-cthoxy-bcnzoic acid. 3-nitro-2-crcsol-5-sullonic acid. 5-nitro-barbituric acid.

4-nitro-bcnzaldehydc. -nitro-phcnol.

Picric acid.

Picryl-chloridc. 2,4,7-trinitrolluorcnonc. 1,3,5-trinitro-benzcne. 1-chlcro-2-mcthyl-anthraquinonc. Duroqninone. 2,6-dichloro-quinonc. 1,5-diphenoxy-anthraquinonc.

2,7-dinitro-anthraquinonc. 1,5-dichloro-anthraquinone.

1,4-dimethyl-anthraquinonc.

2,5-dicliloro-benzoquinonc. 2,3-dichloro-naphthoquinonc-l,4.

1,5-dichloro-anthraquinonc. 1-metl1yl-4-chloro-anthraquinone. 2-methylanthraquinonc. Naphtlioquinone-1,2. 4-nitr0-accnaphthcne. Naphthoquiuonc-IA. Pcntacenc-quinonc. Tctracenc-7,12-quin0ne. 1,4-tolu-quinone. 2,5,7,l0-tctraehloro-pyrene-quinonc.

The quantity of activator which is advantageously added to the photoconductors can be easily determined by simple experiments. It varies according to the substance applied and usually amounts from about 0.1 to about 100 moles, preferably from about 1 to about 50 moles, based on 1000 moles of photoconductive substance. Mixtures of several activator substances can also be used. a In addition to these substances, dye-stufi sensitizers also may be added.

By the addition of the activating substances, photoconductive layers can be produced which are highly lightsensitive, especially within the ultraviolet range, and which are practically colorless. By means of these substances it is also possible to strongly activate the photoconductive layers within the ultraviolet range, whereupon a high sensitivity of the photoconductive layers within the range of visible light can be obtained by a very small addition of optical sensitizers, without sufiicient of the dyestufi sensitizers being added as to result in a highly colored layer. Additions of less than 0.01 percent of the dyestuff sensitizers are effective; in general, however, quantities of from 0.01 to 5 percent, preferably 0.05 to 3 percent, of the dyestufi sensitizers are added.

Additions of larger quantities are possible but in this case no appreciable increase in the sensitivity will, in general, be achieved. It the dyestuff sensitizers are used without the addition of activators, it will be advisable generally to use quantities approaching the upper limits I 785, page 329), Acid Violet 6 B (No. 831, page 351);

xanthene dyestuffs, namely rhoadmines, such as Rhodamine B (No. 864, page 365), Rhodamine 6 G (No. 866, page 366), Rhodamine G Extra (No. 865, page 366), Sulphorhodamine B (No. 863, page 364) and Fast Acid Eosin G (No. 870, page 368), as also phthaleins such as Eosin S (No. 883, page 375), Eosin A (No. 881, page 374), Erythrosin (No. 886, page 376), Phloxin (No. 890, page 378), Bengal Rose (No. 889, page 378), and Fluorescein (No. 880, page 373); thiazine dyestufis such as Methylene Blue (No-1038, page 449); acridine dyestufis such as Acridine Yellow (No. 901, page 383), Acridine Orange (No. 908, page 387) and Trypaflavine (No. 906, page 386); quinoline dyestufis such as Pinacyanol (No. 924, page 396) and cryptocyanine (No. 927, page 397); cyanine dyestuffs e.g. cyanine (No. 921, page 394) and chlorophyll. By the procedure of the present invention, negatives of the master are produced, in which even large black areas are uniformly colored. Practically speaking, the layers show no marginal effects.

The invention will be further illustrated by reference to the following specific examples:

Example I To a solution consisting of 1 part by weight of 2,5-bis- (4'-diethylamino-phenyl (1')) 1,3,4-oxadiazole and 1 part by weight of a ketone resin having a melting range from l-l20 C., a dye number of 0-2 and an acid number of 0, dissolved in 28.parts by weight of ethyleneglycol monomethylether, there is added 0.15 part by weight of beeswax, dissolved in 2 parts by weight of carbon tetrachloride. The mixture is coated onto a paper foil, the surface of which had been pretreated to prevent the penetration of organic solvents, and dried. By means of a corona discharge of 6000 to 7000 volts, the coated paper is positively charged, subsequently exposed to light under a master by means of a high pressure mercury lamp and finally dusted over with a developer consisting of 100 parts by weight of tiny glass balls and 2.5 parts by weight of a toner having a particle size of 20 to 50 and prepared by melting together, grinding, and sieving the following materials:

30 parts by weight of a soluble polystyrene,

30 parts by weight of a maleic resin having a melting range from 95 to 110 C., an acid number of 20-25 and the dye designation extrabright to 35, and

3 parts by weight of carbon black (obtained from natural gas by impingement process).

Example 11 10 parts by weight Off a soluble after-chlorinated polyvinyl chloride and 10 parts by weight of 2,5-bis-(4-N,N- diethylamino phenyl-(l'))-1,3,4-triazole are dissolved in a mixture of 100 parts by weight of methylethylketone and 20 parts by weight of toluene. To this solution, there is added, first, 0.8 part by weight of montan wax, dissolved in 30 parts by weight of carbon tetrachloride, and then a solution of 0.004 part by weight of ethyl violet (Schul'tz Farbstofiitabellen, 7th edition, vol. 1 (1931), No. 787) in 2 parts by weight of methanol. By means of a casting device, a paper base is mechanically coated with the solution thus obtained. After the paper has been dried, it is given a positive charge by means of a corona discharge and then a latent image of a book page printed on both sides is produced on the coated paper by 1 means of an episcopic process.

The latent image is developed with the developer powder described in Example I. The finely divided resin adheres to those parts of the layer which were struck by light during exposure and the reversed image thus obtained is fixed by heating.

Example 111 1. part by weight of 2-(4'-dimethylaminophenyl)-4,5- diphenylimidazole, 1 part by weight of a styrene copolymer containing carboxyl groups, having a decomposition point between 200-240 C. and a specific gravity of 1.26-1.28, and 0.1 part by weight of a synthetic wax (Wachs KP) are dissolved in a solvent mixture consisting of 15 parts by weight of benzene, 15 parts by weight of methylethylketone, and 2 parts by weight of carbon tetrachloride; the solution is coated onto an aluminum foil. After evaporation of the solvent, a layer is formed which adheres firmly to the surface of the foil. By further treating the aluminum foil as described in Example I, and by developing the electrophotographic copies by means of a developer consisting of sodium chloride crystals and a carbon black-resin mixture, a reversed image of the original is produced on the aluminum foil, which is fixed by heating or by a treatment with trichloroethylene vapors. The aluminum foil carrying the image can be converted into a printing plate by wiping it over with a solution consisting of 5 percent of monoethanol amine, 5 percent of dieth-anol amine, 10 percent of glycerine, 5 percent of sodium silicate, and 75 percent of polyethylene glycol, briefly rinsing with water, and inking with greasy (1') )-1,3,4-oxadiazole, 10 parts by weight of a synthetic wax (Wachs O) and 0.01 part by weight of Victoria Blue B (Schultz Farbstofitabellen, No. 822) are dissolved in a mixture consisting of 50 pants by weight of toluene, 100

parts by weight of carbon tetrachloride, and 30 parts by weight of methanol. The solution is coated onto transparent paper, the surface of which had been pretreated to prevent the penetration of organic solvents, and is then dried. After the paper has been given a positive electric charge by means of a corona discharge, it is exposed under a master. By means of a bar magnet, iron filings dipped into a carbon black-resin mixture are evenly distributed over the latent image. The carbon black-resin mixture adheres to the latent image and a reversed image of the master used becomes visible, which is fixed by heating. The images, which are distinguished by very good full tones, may be used as intermediate originals for making further copies, e.g. on blue print paper.

Example V 1 part by weight of 4,S-bis-4'-chlorophenylimidazolone- (2) and 1 part by weight Off a zinc resinate having a melting point of 130 C., an acid number of 35-40 and a dye number of 210-230, are dissolved in 30 parts by weight of ethyleneglycol monomethylether. To this solution, there is added a solution of 1 part by weight of carnauba wax in parts by weight of carbon tetrachloride and the mixed solution is used for coating a paper base, which had been pretreated to prevent the penetration of organic solvents. After it has been provided with a positive charge, by means of a corona discharge, the paper is exposed under a master and developed as described in Example I. The reversed image thus obtained is fixed by heating.

Example V1 12 parts by weight of a soluble after-chlorinated polyvinyl chloride and 10 parts by weight of anthracene are dissolved in a mixture of 100 parts by weight of methylethylketone and parts by weight of toluene. To this solution, there is added a solution of 1 part by weight of montan wax in parts by volume of carbon tetrachloride. The solution thus obtained may be used for mechanically coating, by means of a hopper device, a paper base, which had been pretreated to prevent the penetration of organic solvents. After drying, the paper is positively charged by means of a corona discharge, exposed under a master, and treated with a developer as described in Example I. The finely divided resin adheres to those parts of the layer which were struck by light during exposure; a reversed image becomes visible which is fixed by heating.

Example VII 1 part by weight of Fluorol 6G, 1 part by weight of a ketone resin having a melting range of from 76 to 82 C., a dye number of 1-2.5 and an acid number of 0, and 0.15 part by Weight of a synthetic wax (Wachs KP) are dissolved in a solvent mixture consisting of 15 parts by weight of benzene, 15 parts by weight of methylethylketone and 2 parts by weight of carbon tetrachloride. The solution thus formed is coated onto an aluminum foil. After evaporation of the solvent, a layer remains which adheres firmly to the surface of the foil. By following the procedure described in Example I, a reversed image of the master is produced on the alu minum foil.

Example VIII 10 parts by weight of polyvinyl carbazole are dissolved in 150 parts by weight of toluene. The solution is coated onto paper, the surface of which has been pretreated to prevent the penetration of organic solvents, and is dried. The dry layer is provided with a thin coating of beeswax, by polishing with the wax and then rubbing with a clean dry cloth. The thus coated paper iS further treated as described in Example I. A reversed image of the master used is obtained which is fixed by moderate heating.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the prescut invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is: I

1. A photographic reproduction process for the production of reversed images of improved coverage which comprises exposing an electrostatically charged supported homogeneous photoconductive insulating layer comprising an organic photoconductor and a wax to light under a master and developing the resulting electrostatic latent image by contact with a developer containing particlcs having an electric charge of the same polarity as that of the electrostatic latent image.

2. A process according to claim 1 in which the wax is a synthetic wax.

3. A process according to claim 1 in which the wax is a natural wax.

4. A process according to claim 1 in which the photoconductive insulating layer also contains an activator.

5. A process according to claim 1 in which the photoconductive insulating layer also contains a sensitizer.

6. A process according to claim 1 in which the photoconductor is 2,5-bis- (4-diethylamino-pl1enyl-( 1') )-1,3, 4-oxadiazole.

7. A process according to claim 1 in which the photoconductor is 2,5-bis-(4'-N,N-diethylamino phenyl-(1))- 1,3,4-triazole.

8. A process according to claim 1 in which the photoconductor is 2-(4'-dimethylaminophenyl)-4,5-diphenyl- I toconductor is 4,5-bis-4-chlorophenyl-imidazolone-(2).

11. A process according to claim 1 in which the photoconductor is anthracene.

12. A process according to claim 1 in which the photoconductor is polyvinyl carbazole.

13. A process according to claim 1 in which the insulating layer includes a resin.

14. A process according to claim 1 in which the support is paper.

15. A process according to claim 1 in which the support is aluminum.

16. A process according to claim 1 in which the wax is beeswax.

17. A process according to claim 1 in which the wax is montan wax.

18. A process according to claim 1 in which the Wax is carnauba wax.

19. A photographic reproduction process for the production of reversed images of improved coverage which comprises exposing an electrostatically charged supported homogeneous photoconductive insulating layer comprising an organic photoconductor, said layer having a layer of wax thereon, to light under a master and developing the resulting electrostatic latent image by contact with a developer containing particles having an electric charge of the same polarity as that of the electrostatic latent image.

References Cited in the file of this patent UNITED STATES PATENTS 2,297,691 Carlson Oct. 6, 1942 2,663,636 Middleton Dec. 22, 1953 2,758,939 Sugarman Aug. 14, 1956 2,862,815 Sugarman et al. Dec. 2, 1958 2,901,348 Dessauer et al. Aug. 25, 1959 2,940,848 Kosteles et al. June 14, 1960 3,005,707 Kallman et al. Oct. 21, 1961 3,072,479 Bethe Jan. 8, 1963 3,079,253 Greig Feb. 26, 1963 FOREIGN PATENTS 201,301 Australia Mar. 19, 1956 

1. A PHOTOGRAPHIC REPRODUCTION PROCESS FOR THE PRODUCTION OF REVERSED IMAGES OF IMPROVED COVERAGE WHICH COMPRISES EXPOSING AN ELECTROSTATICALLY CHARGED SUPPORTED HOMOGENEOUS PHOTOCONDUCTIVE INSULATING LAYER COMPRISING AN ORGANIC PHOTOCONDUCTOR AND A WAX TO LIGHT UNDER A MASTER AND DEVELOPING THE RESULTING ELECTROSTATIC LATENT IMAGE BY CONTACT WITH A DEVELOPER CONTAINING PARTICLES HAVING AN ELECTRIC CHARGE OF THE SAME POLARITY AS THAT OF THE ELECTROSTATIC LATENT IMAGE. 